This section starts to examine the configuration of the Cisco ASA and covers the fundamentals for providing basic connectivity and device management. This section covers basic command-line interface (CLI) configuration, but mainly focuses on configuring the ASA through the graphical Adaptive Security Device Manager (ASDM).

This chapter is from the book

This chapter is from the book

This section starts to examine the configuration of the Cisco ASA and covers the fundamentals for providing basic connectivity and device management. This section covers basic command-line interface (CLI) configuration, but mainly focuses on configuring the ASA through the graphical Adaptive Security Device Manager (ASDM).

CLI and ASDM Connection

You can configure a Cisco ASA in two ways: through the CLI or through the ASDM.

Both the CLI and ASDM offer benefits for configuration, and people disagree as to the best method. The CLI versus GUI configuration argument has been around since the days of UNIX versus Windows. The CLI is fast, after you have mastered it, but the GUI is intuitive and easier to configure, especially with the wizard quick-configuration options now available.

Proponents of the ASDM point to the various configuration wizards that exist within the ASDM that are not available via the CLI alone. The logging and monitoring functionality that the ASDM provides cannot be replicated within the CLI. Today, only a very few commands must be performed from the CLI. The ASDM can be used for all other configurations.

Command-Line Interface

The CLI is the historic way in which all Cisco devices were configured. This is a command-based interface similar to a UNIX- or DOS-based operating system. For many Cisco devices, the CLI must be used to initially “bootstrap” the device for inclusion into the exiting network infrastructure.

Commands are typed through a terminal connection to the ASA, and these are then written to the configuration. The CLI is powerful and fast, but learning how to use the CLI is like learning another language.

You can either connect to the CLI through the console port using a console cable or by using Telnet or Secure Shell (SSH). A Cisco console cable is provided with every ASA because this is the normal initial method to connect to the device for the initial configuration.

Using a console cable is an out-of-band connection, and using Telnet or SSH is an in-band connection.

NOTE

Because Telnet is sent in clear text and SSH is an encrypted session, you should always use SSH to connect to any network device.

When you first purchase an ASA, you need to configure the ASA through the CLI to configure the initial network settings that enable you to connect to the device using ASDM, which is provided through a web interface, so basic IP settings need to be initially configured.

When you initially connect to an ASA, you are greeted with the following prompt:

ciscoasa>

This is an unprivileged mode (or user mode) and is represented by the > after the hostname.

Entering enable at this prompt places you in privileged EXEC mode, and you see the following prompt:

ciscoasa#

From privileged EXEC mode, you can then enter the configuration mode to enter configuration commands into the ASA. The show and debug commands to monitor and troubleshoot the ASA are also entered in privileged EXEC mode. This is similar to the EXEC modes found within IOS on a Cisco router or switch. Note that Cisco is taking great pains to try and standardize the operating systems behaviors and commands across all of their different network devices.

NOTE

You can use the quickconfiguration system to configure the initial parameters of the ASA to facilitate ASDM connection, but the basic configuration commands without using the quick configuration are provided.

ASDM

ASDM is an acronym for the ASA Security Device Manager (ASDM), which it is the main graphical way to configure, manage, and monitor your ASA firewall.

You access the ASDM through a web browser. ASDM is a Java-based application, so any modern browser that supports Java will suffice (for instance, Safari, Firefox, Chrome, or Internet Explorer). The connection to ASDM is over SSL, so the configuration is always encrypted between the client and the ASA through the web browser.

Because you have to connect to ASDM through a browser interface, you must configure an IP address on the inside interface to enable you to connect your browser to it. The next section covers interface configuration in more depth.

In addition to setting the IP address, you must enter some other basic configuration commands via the CLI to the ASA to configure the initial connection to the ASDM.

Let’s now run through the necessary commands on an ASA that has a default blank configuration. The commands shown are the bare minimum to enable a connection to the ASDM and are as far as you need to take the CLI in most cases. Because this is an ASA with a blank configuration, the only way to connect is via the CLI using a serial connection.

The first step is to assign an IP address to the inside interface of the ASA. The inside interface is the interface on the inside or trusted part of your network. The outside interface is the interface on the outside or untrusted part of your network.

To enter these configuration commands, you need to be in configuration mode on the ASA. From this point forward, you should be in configuration mode; the prompt shows which configuration mode is required:

For these examples, the configuration from a Cisco ASA 5505 is used, which has a built-in eight-port switch with no fixed interfaces. IP addresses on the ASA 5505 are configured to VLAN interfaces, and then the VLANs are assigned to the Ethernet interfaces. For other ASA models, the IP address is added straight to the corresponding Ethernet interface.

Because this VLAN is going to be the inside network, you now need to name the VLAN interface as the inside interface:

Ciscoasa(config-if)# nameif inside
INFO: Security level for "inside" set to 100 by default.

When the nameif command is entered, because the value is inside, the default security level of 100 is attributed to the VLAN interface. In contrast to this, the default security level of 0 will be applied to the interface if you name the interface outside. Security levels are reviewed later in this Quick Reference.

VLAN1 is now configured as the inside interface with the IP address of 192.168.1.254/24. By default, all ports are in VLAN1, so you now need to tell the ASA 5505 which physical Ethernet port is the inside connection. In this example, you use Ethernet0/1 as the inside interface. So, enter the following commands to bring up Ethernet0/1 because, by default, all ports are in an administrative shutdown mode:

You can see that the interface is up. You can now ping the inside interface of the ASA 5505 from a workstation connected to the 192.168.1.0/24 network and ping workstations on the 192.168.1.0/24 network from the ASA 5505.

The next step is to configure a secure password on the ASA. You can provide access to the web-based administration interface of the ASA, so ensure that it is protected and locked down with authentication.

By default, no password is set on the ASA, and anybody can connect to it via the console connection if they have physical access to the device.

Set an enable password on the ASA:

ciscoasa(config)# enable password securepassword

The preceding line creates the enable password securepassword. Obviously, you want to replace this with a secure, strong password in line with your corporate password policy.

At this point, the interface is up and has a valid IP address configured. However, you must complete a couple more steps to facilitate a connection to the ASDM. Running a browser to https://192.168.1.254 at this point returns with a Page Not Found error message.

The ASA has a built-in web server. This is what serves the ASDM to users requesting it through their browsers. By default, this web server is not enabled.

You can enable the internal web server in the ASA with the following command:

ciscoasa(config)# http server enable

This enables the HTTP server on the ASA, but if you try a connection to the ASDM, you still cannot connect. This failure to connect results because the ASA operates in a closed policy, unlike the HTTPS server on a router.

On the ASA, all connections to the HTTP server are denied by default, and you must enter a configuration command to specify the IP addresses that are allowed to access the ASDM. On a router, by default all IP addresses can connect to the HTTP server, and you must create an access list to restrict this access.

In this example, you want to allow the entire inside network access to the ASDM:

ciscoasa(config)# http 192.168.1.0 255.255.255.0 inside

The preceding command enables all hosts on the 192.168.1.0/24 network, which is located on the inside interface, access to the ASDM. In the real world, it is recommended that administrative access be locked down to specific management hosts, by using explicit host IP address entries.

Connecting now with a web browser to https://192.168.1.254 displays the initial ASDM connection screen, as shown in Figure 7.